Heretofore, as shown particularly in U.S. Pat. No. 5,433,119 dated Jul. 18, 1995, a positive displacement hydraulic motor is utilized to screw a pile in the ground. It is desirable to have an indication of the torque applied to the screw pile or anchor as the level of torque required to turn the new pile is indicative of the strength of the soil and may be used to estimate the capacity of the soil. Low installation torque indicates a weak soil and low pile capacity, whereas a high installation torque indicates a relatively strong soil and greater pile capacity. Where the required installation torque can be accurately measured, the approximate holding capacity of a new pile can be reliably predicted.
A torque indicator system is illustrated in U.S. Pat. No. 5,433,119 for measuring the torque output of a positive displacement hydraulic motor that operates to screw a foundation pile into the ground. The pressure drop across the hydraulic motor is indicated on the gauge for a visual display of the torque output. However, there is no control over the amount of torque provided by the motor. It is desired to protect the motor from an unusually high output torque and also to limit the torque applied by the motor against the screw for rotating the anchor pile as damage could result. Thus, it is desired that the torque output of the hydraulic motor be controlled and limited to a predetermined amount.
It is an object of the present invention to provide a fluid pressure control system to limit the output torque of a positive placement hydraulic motor to a selected amount for rotating a member in the ground.